Electric arc welder system with waveform profile control

ABSTRACT

An electric arc welder for creating a succession of AC waveforms between an electrode and workpiece by a power source comprising an high frequency switching device for creating individual waveforms in the succession of waveforms. Each of the individual waveforms has a profile determined by the magnitude of each of a large number of short current pulses generated at a frequency of at least 18 kHz by a pulse width modulator with the magnitude of the current pulses controlled by a wave shaper. The welder is provided with a profile control network for setting more than one profile parameter selected from the class consisting of frequency, duty cycle, up ramp rate and down ramp rate and a magnitude circuit for adjusting the waveform profile to set total current, voltage and/or power.

The present invention relates to the art of electric arc welding andmore particularly to an electric arc welder with waveform profilecontrol.

INCORPORATION BY REFERENCE

The present invention is directed to an electric arc welder systemutilizing high capacity alternating circuit power sources for drivingtwo or more tandem electrodes of the type used in seam welding of largemetal blanks. It is preferred that the power sources use the switchingconcept disclosed in Stava U.S. Pat. No. 6,111,216 wherein the powersupply is an inverter having two large output polarity switches with thearc current being reduced before the switches reverse the polarity.Consequently, the term “switching point” is a complex procedure wherebythe power source is first turned off awaiting a current less than apreselected value, such as 100 amperes. Upon reaching the 100 amperethreshold, the output switches of the power supply are reversed toreverse the polarity from the D.C. output link of the inverter. Thus,the “switching point” is an off output command, known as a “kill”command, to the power supply inverter followed by a switching command toreverse the output polarity. The kill output can be a drop to adecreased current level. This procedure is duplicated at each successivepolarity reversal so the AC power source reverses polarity only at a lowcurrent. In this manner, snubbing circuits for the output polaritycontrolling switches are reduced in size or eliminated. Since thisswitching concept is preferred to define the switching points as used inthe present invention, Stava U.S. Pat. No. 6,111,216 is incorporated byreference. The concept of an AC current for tandem electrodes is wellknown in the art. U.S. Pat. No. 6,207,929 discloses a system wherebytandem electrodes are each powered by a separate inverter type powersupply. The frequency is varied to reduce the interference betweenalternating current in the adjacent tandem electrodes. Indeed, thisprior patent of assignee relates to single power sources for drivingeither a DC powered electrode followed by an AC electrode or two or moreAC driven electrodes. In each instance, a separate inverter type powersupply is used for each electrode and, in the alternating current highcapacity power supplies, the switching point concept of Stava U.S. Pat.No. 6,111,216 is employed. This system for separately driving each ofthe tandem electrodes by a separate high capacity power supply isbackground information to the present invention and is incorporatedherein as such background. In a like manner, U.S. Pat. No. 6,291,798discloses a further arc welding system wherein each electrode in atandem welding operation is driven by two or more independent powersupplies connected in parallel with a single electrode arc. The systeminvolves a single set of switches having two or more accurately balancedpower supplies forming the input to the polarity reversing switchnetwork operated in accordance with Stava U.S. Pat. No. 6,111,216. Eachof the power supplies is driven by a single command signal and,therefore, shares the identical current value combined and directedthrough the polarity reversing switches. This type system requires largepolarity reversing switches since all of the current to the electrode ispassed through a single set of switches. U.S. Pat. No. 6,291,798 doesshow a master and slave combination of power supplies for a singleelectrode and discloses general background information to which theinvention is directed. For that reason, this patent is also incorporatedby reference. An improvement for operating tandem electrodes withcontrolled switching points is disclosed in Houston U.S. Pat. No.6,472,634. This patent is incorporated by reference.

BACKGROUND OF INVENTION

Welding applications, such as pipe welding, often require high currentsand use several arcs created by tandem electrodes. Such welding systemsare quite prone to certain inconsistencies caused by arc disturbancesdue to magnetic interaction between two adjacent tandem electrodes. Asystem for correcting the disadvantages caused by adjacent AC driventandem electrodes is disclosed in Stava U.S. Pat. No. 6,207,929. In thatprior patent, each of the AC driven electrodes has its own inverterbased power supply. The output frequency of each power supply is variedso as to prevent interference between adjacent electrodes. This systemrequires a separate power supply for each electrode. As the currentdemand for a given electrode exceeds the current rating of the inverterbased power supply, a new power supply must be designed, engineered andmanufactured. Thus, such system for operating tandem welding electrodesrequire high capacity or high rated power supplies to obtain highcurrent as required for pipe welding. To decrease the need for specialhigh current rated power supplies for tandem operated electrodes,assignee developed the system disclosed in Stava U.S. Pat. No. 6,291,798wherein each AC electrode is driven by two or more inverter powersupplies connected in parallel. These parallel power supplies have theiroutput current combined at the input side of a polarity switchingnetwork. Thus, as higher currents are required for a given electrode,two or more parallel power supplies are used. In this system, each ofthe power supplies are operated in unison and share equally the outputcurrent. Thus, the current required by changes in the welding conditionscan be provided only by the over current rating of a single unit. Acurrent balanced system did allow for the combination of several smallerpower supplies; however, the power supplies had to be connected inparallel on the input side of the polarity reversing switching network.As such, large switches were required for each electrode. Consequently,such system overcame the disadvantage of requiring special powersupplies for each electrode in a tandem welding operation of the typeused in pipe welding; but, there is still the disadvantage that theswitches must be quite large and the input, paralleled power suppliesmust be accurately matched by being driven from a single current commandsignal. Stava U.S. Pat. No. 6,291,798 does utilize the concept of asynchronizing signal for each welding cell directing current to eachtandem electrode. However, the system still required large switches.This type of system was available for operation in an ethernet networkinterconnecting the welding cells. In ethernet interconnections, thetiming cannot be accurately controlled. In the system described, theswitch timing for a given electrode need only be shifted on a timebasis, but need not be accurately identified for a specific time. Thus,the described system requiring balancing the current and a single switchnetwork has been the manner of obtaining high capacity current for usein tandem arc welding operations when using an ethernet network or aninternet and ethernet control system. There is a desire to controlwelders by an ethernet network, with or without an internet link. Due totiming limitation, these networks dictated use of tandem electrodesystems of the type using only general synchronizing techniques.

Such systems could be controlled by a network; however, the parameter toeach paralleled power supply could not be varied. Each of the cellscould only be offset from each other by a synchronizing signal. Suchsystems were not suitable for central control by the internet and/orlocal area network control because an elaborate network to merelyprovide offset between cells was not advantageous. Houston U.S. Pat. No.6,472,634 discloses the concept of a single AC arc welding cell for eachelectrode wherein the cell itself includes one or more paralleled powersupplies each of which has its own switching network. The output of theswitching network is then combined to drive the electrode. This allowsthe use of relatively small switches for polarity reversing of theindividual power supplies paralleled in the system. In addition,relatively small power supplies can be paralleled to build a highcurrent input to each of several electrodes used in a tandem weldingoperation. The use of several independently controlled power suppliesparalleled after the polarity switch network for driving a singleelectrode allows advantageous use of a network, such as the internet orethernet.

In Houston U.S. Pat. No. 6,472,634, smaller power supplies in eachsystem are connected in parallel to power a single electrode. Bycoordinating switching points of each paralleled power supply with ahigh accuracy interface, the AC output current is the sum of currentsfrom the paralleled power supplies without combination before thepolarity switches. By using this concept, the ethernet network, with orwithout an internet link, can control the weld parameters of eachparalleled power supply of the welding system. The timing of the switchpoints is accurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1-5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The Houston U.S. Pat. No.6,472,634 system is especially useful for paralleled power supplies topower a given electrode with AC current. The switch points arecoordinated by an accurate interface and the weld parameter for eachparalleled power supply is provided by the general information network.This background is technology developed and patented by assignee anddoes not necessarily constitute prior art just because it is herein usedas “background.”

As a feature of the system in Stava U.S. Pat. No. 6,207,929, two or morepower supplies can drive a single electrode. Thus, the system comprisesa first controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and ethernet or a local areaethernet network. The timing accuracy of the digital interface is lessthan about 10 μs and, preferably, in the general range of 1-5 μs. Thus,the switching points for the two controllers driving a single electrodeare commanded within less than 5 μs. Then, switching actually occurswithin 25 μs. At the same time, relatively less time sensitiveinformation is received from the information network also connected tothe two controllers driving the AC current to a single electrode in atandem welding operation. The 25 μs maximum delay can be changed, but isless than the switch command accuracy.

The unique control system disclosed in Houston U.S. Pat. No. 6,472,634is used to control the power supply for tandem electrodes used primarilyin pipe seam welding and disclosed in Stava U.S. Pat. No. 6,291,798.This Stava patent relates to a series of tandem electrodes movable alonga welding path to lay successive welding beads in the space between theedges of a rolled pipe or the ends of two adjacent pipe sections. Theindividual AC waveforms used in this unique technology are created by anumber of current pulses occurring at a frequency of at least 18 kHzwith a magnitude of each current pulse controlled by a wave shaper. Thistechnology dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping ofthe waveforms in the AC currents of two adjacent tandem electrodes isknown and is shown in not only the patents mentioned above, but in StavaU.S. Pat. No. 6,207,929. In this latter Stava patent, the frequency ofthe AC current at adjacent tandem electrodes is adjusted to preventmagnetic interference. All of these patented technologies by The LincolnElectric Company of Cleveland, Ohio have been advances in the operationof tandem electrodes each of which is operated by a separate AC waveformcreated by the waveform technology set forth in these patents. Thesepatents are incorporated by reference herein. However, these patents donot disclose the present invention which is directed to the use of suchwaveform technology for use in tandem welding by adjacent electrodeseach using an AC current. This technology, as the normal transformertechnology, has experienced difficulty in controlling the dynamics ofthe weld puddle. Thus, there is a need for an electric arc weldingsystem for adjacent tandem electrodes which is specifically designed tocontrol the dynamics and physics of the molten weld puddle during thewelding operation. These advantages can not be obtained by merelychanging the frequency to reduce the magnetic interference.

THE INVENTION

The present invention relates to an improvement in the waveformtechnology disclosed in Blankenship U.S. Pat. No. 5,278,390 and used fortandem electrode welding systems by several patents, including StavaU.S. Pat. No. 6,207,929; Stava U.S. Pat. No. 6,291,798; and, HoustonU.S. Pat. No. 6,472,634. The improvement over this well developedtechnology is to control on a real time basis the individual ACwaveforms generated between the electrode and workpiece which waveformsin succession constitute the welding process. By using the presentinvention each individual waveform in the AC welding process iscontrolled in a unique manner that adjusts several profile parametersand also the energy profile of the individual sections of the waveform.In this manner, various welding currents and/or voltage waveforms can beused to effect the overall welding process in a unique manner thataccurately controls the process using waveform technology of the typepioneered by The Lincoln Electric Company of Cleveland, Ohio. By usingthe present invention, the welding process can be controlled to effectseveral characteristics such as penetration into the base metal, themelt off rate of the electrode, the heat input into the base metal, andthe welding travel speed as well as the wire feed speed. In addition,various arc welding current and/or arc welding voltage waveforms can begenerated to essentially “paint” a desired waveform to effect themechanical and metallurgical properties of the “as welded” weld metalresulting from the welding process. The invention controls the generalprofile of a waveform which means the parameters defining the profileare controlled. Then the energy or power of the profile controlledwaveform can be adjusted without changing the general profile which isfixed.

When combining various welding waveforms, sometimes called wave shapes,with specific electrodes, an improvement in the welding process both inwelding speed and improved mechanical metallurgical properties isobtained. The types of electrode that are combined with the uniqueprofile controlled waveforms are solid wires normally used for lowcarbon steel, solid wires of various alloys such as, but not limited to,nickel and chrome for welding stainless steel and other similar alloys,aluminum electrodes and cored electrodes including internal flux andmetal alloys. By selecting the desired welding wire and then using thepresent invention to “paint” the exactly controlled general profile ofan individual waveform in a succession of waveforms constituting thewelding process, the welder using the present invention can produceheretofore unobtainable weld results.

In the past, the ability to use SCR welders to produce AC waveforms ofaccurately and varied shapes is technically difficult, if notimpossible. The present invention utilizes the high frequency waveformtechnology using an inverter or an equivalent chopper and/or design,which designs have the capacity of generating virtually any waveformprofile. The waveform profile of successive waveforms in an AC weldingprocess usually involves producing current pulses at a rate exceeding 18kHz to enable the generation of a waveform by adding or subtractingsmall amounts of energy. The present invention uses this technology bycontrolling the general profile of individual waveforms. The inventionproduces an AC waveform with a controlled profile, whereas normally suchtechnology was used to produce DC or pulse DC waveforms. When thetechnology was used before to create AC waveforms, the waveforms werefixed and normally square wave. Such square waves were normally notimbalanced AC waveforms because the control concept was not directed toprofile parameters, but to pulse wave magnitude. The present inventionprovides an improvement to a welder using high switching speed waveformtechnology which improvement allows the individual waveforms to becreated in virtually any desired profile by controlling a set of profileparameters. In this manner, the exact general profile of a waveform canbe combined with the precise welding electrode or wire to produce thedesired welding characteristics of a welding process, particularly anautomatic weld process such as implemented by a robotic cell. Theprofile is combined with a magnitude circuit to change magnitude toadjust heat while holding the exact set general profile.

In accordance with the present invention there is provided an electricarc welder for creating a succession of AC waveforms between anelectrode and a workpiece by a power source comprising an high frequencyswitching device such as an inverter or its equivalent chopper forcreating individual waveforms in the succession of waveformsconstituting the welding process. Each of the individual waveforms has aprecise general profile determined by the magnitude of each of a largenumber of short current pulses generated at a frequency of at least 18kHz by a pulse width modulator with the magnitude of the current pulsescontrolled by a wave shaper. The polarity of any portion of theindividual AC waveform is determined by the data of a polarity signal. Aprofile control network is used for establishing the general profile ofan individual waveform by setting more than one profile parameter of theindividual waveform. The parameters are selected from the classconsisting of frequency, duty cycle, up ramp rate and down ramp rate.Also included in the welder control is a magnitude circuit for adjustingthe individual waveform profile to set total current, voltage and/orpower for the waveform without substantially changing the set generalprofile. This concept of the invention is normally accomplished in twosections where the energy is controlled in the positive polarity and inthe negative polarity of the generated waveform profile.

In accordance with another aspect of the present invention there isprovided a method of electric arc welding by creating a succession of ACwaveforms between an electrode and a workpiece by a power sourcecomprising an high frequency switching device for creating individualwaveforms in the succession of waveforms constituting the weld process.Each of the individual waveforms has profile determined by the magnitudeof each of a large number of short current pulses generated at afrequency of at least 18 kHz by a pulse width modulator with themagnitude of the current pulses controlled by a wave shaper. The methodcomprises determining the plurality of any portion of the individualwaveform by the data of a plurality signal, establishing the generalprofile of an individual waveform by setting more than one profileparameter of an individual waveform, said parameters selected from theclass consisting of frequency, duty cycle, up ramp rate and down ramprate and adjusting the waveform to set the total magnitude of current,voltage and/or power without substantially changing the set profile.

The primary object of the present invention is the provision of anelectric arc welder using waveform technology wherein the generalprofile of the individual waveforms constituting the AC welding processis accurately controlled to a given profile that will precisely performa welding process with desired physical and metallurgicalcharacteristics.

Another object of the present invention is the provision of an electricarc welder, as defined above, which electric arc welder generates aprecise controllable and changeable general profile for the waveform ofan AC welding process to thereby adjust the weld speed, deposition rate,heat input, mechanical and metallurgical properties and relatedcharacteristics to improve the quality and performance of the weldingprocess.

Yet another object of the present invention is the provision of anelectric arc welder, as defined above, which electric arc weldersimultaneously adjusts more than one profile parameter of an individualwaveform where the parameters are selected from the class consisting offrequency, duty cycle, up ramp rate and down ramp rate.

Still a further object of the present invention is the provision of anelectric arc welder, as defined above, which electric arc welderincludes a magnitude circuit control for adjusting the individualwaveform profile to set total current voltage and/or power for each ofthe polarity portions of the waveform constituting the AC weldingprocess without substantially changing the set waveform profile.

Yet another object of the present invention is the provision of a methodfor arc welding that creates a succession of AC waveforms between anelectrode and workpiece, which method accurately and interactively setsthe general profile of the individual waveform constituting the ACwelding process.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a welding system that can be used toperform the present invention;

FIG. 2 is a wiring diagram of two paralleled power sources, each ofwhich include a switching output and can be used in practicing theinvention;

FIG. 3 is a cross sectional side view of three tandem electrodes of thetype controllable by the power source disclosed in FIGS. 1 and 2;

FIG. 4 is a schematic layout in block form of a welding system for threeelectrodes using the disclosure in Houston U.S. Pat. No. 6,472,634 andStava U.S. Pat. No. 6,291,798 and where one of the three power sourcesis used in practicing the invntion as shown in FIGS. 17 and 18;

FIG. 5 is a block diagram showing a single electrode driven by thesystem as shown in FIG. 4 with a variable pulse generator disclosed inHouston U.S. Pat. No. 6,472,634 and used for practicing the presentinvention;

FIG. 6 is a current graph for one of two illustrated synchronizingpulses and showing a balanced AC waveform for one tandem electrode;

FIG. 7 is a current graph superimposed upon a polarity signal havinglogic to determine the polarity of the waveform as used in a welder thatcan practice the present invention;

FIG. 8 is a current graph showing a broad aspect of a waveform with aprofile controllable by the present invention;

FIGS. 9 and 10 are schematic drawings illustrating the dynamics of theweld puddle during concurrent polarity relationships of tandemelectrodes;

FIG. 11 is a pair of current graphs showing the waveforms on twoadjacent tandem electrodes that can be generated by a background system;

FIG. 12 is a pair of current graphs of the AC waveforms on adjacenttandem electrodes with areas of concurring polarity relationships;

FIG. 13 are current graphs of the waveforms on adjacent tandemelectrodes wherein the AC waveform of one electrode is substantiallydifferent waveform of the other electrode to limit the time ofconcurrent polarity relationships;

FIG. 14 are current graphs of two sinusoidal waveforms for adjacentelectrodes operated by a background system to use different shaped waveforms for the adjacent electrodes;

FIG. 15 are current graphs showing waveforms at four adjacent AC arcs oftandem electrodes shaped and synchronized in accordance with abackground aspect of the invention;

FIG. 16 is a schematic layout of a known software program to causeswitching of the paralleled power supplies as soon as the coordinatedswitch commands have been processed and the next coincident signal hasbeen created;

FIG. 17 is a block diagram of the program used in the computercontroller to improve the background system shown in FIGS. 1-16 so awelder performs in accordance with the preferred embodiment of thepresent invention; and,

FIG. 18 is a schematically illustrated waveform used in explaining theimplementation of the present invention.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, a background system for implementing theinvention is shown in detail in FIGS. 1, 2, 4, 5 and 16. FIGS. 2 and6-15 describe prior attributes of the disclosed background weldingsystems. The improvement of this invention is shown in FIGS. 17 and 18.

Turning now to the background system to which the present invention isan improvement and/or an enhancement, FIG. 1 discloses a single electricarc welding system S in the form of a single cell to create analternating current as an arc at weld station WS. This system or cellincludes a first master welder A with output leads 10, 12 in series withelectrode E and workpiece W in the form of a pipe seam joint or otherwelding operation. Hall effect current transducer 14 provides a voltagein line 16 proportional to the current of welder A. Less time criticaldata, such as welding parameters, are generated at a remote centralcontrol 18. In a like manner, a slave following welder B includes leads20, 22 connected in parallel with leads 10, 12 to direct an additionalAC current to the weld station WS. Hall effect current transducer 24creates a voltage in line 26 representing current levels in welder Bduring the welding operation. Even though a single slave or followerwelder B is shown, any number of additional welders can be connected inparallel with master welder A to produce an alternating current acrosselectrode E and workpiece W. The AC current is combined at the weldstation instead of prior to a polarity switching network. Each welderincludes a controller and inverter based power supply illustrated as acombined master controller and power supply 30 and a slave controllerand power supply 32. Controllers 30, 32 receive parameter data andsynchronization data from a relatively low level logic network. Theparameter information or data is power supply specific whereby each ofthe power supplies is provided with the desired parameters such ascurrent, voltage and/or wire feed speed. A low level digital network canprovide the parameter information; however, the AC current for polarityreversal occurs at the same time. The “same” time indicates a timedifference of less than 10 μs and preferably in the general range of 1-5μs. To accomplish precise coordination of the AC output from powersupply 30 and power supply 32, the switching points and polarityinformation can not be provided from a general logic network wherein thetiming is less precise. The individual AC power supplies are coordinatedby high speed, highly accurate DC logic interface referred to as“gateways.” As shown in FIG. 1, power supplies 30, 32 are provided withthe necessary operating parameters indicated by the bi-directional leads42 m, 42 s, respectively. This non-time sensitive information isprovided by a digital network shown in FIG. 1. Master power supply 30receives a synchronizing signal as indicated by unidirectional line 40to time the controllers operation of its AC output current. The polarityof the AC current for power supply 30 is outputted as indicated by line46. The actual switching command for the AC current of master powersupply 30 is outputted on line 44. The switch command tells power supplyS, in the form of an inverter, to “kill,” which is a drastic reductionof current. In an alternative, this is actually a switch signal toreverse polarity. The “switching points” or command on line 44preferably is a “kill” and current reversal commands utilizing the“switching points” as set forth in Stava U.S. Pat. No. 6,111,216. Thus,timed switching points or commands are outputted from power supply 30 byline 44. These switching points or commands may involve a power supply“kill” followed by a switch ready signal at a low current or merely acurrent reversal point. The switch “ready” is used when the “kill”concept is implemented because neither inverters are to actually reverseuntil they are below the set current. This is described in FIG. 16. Thepolarity of the switches of controller 30 controls the logic on line 46.Slave power supply 32 receives the switching point or command logic online 44 b and the polarity logic on line 46 b. These two logic signalsare interconnected between the master power supply and the slave powersupply through the highly accurate logic interface shown as gateway 50,the transmitting gateway, and gateway 52, the receiving gateway. Thesegateways are network interface cards for each of the power supplies sothat the logic on lines 44 b, 46 b are timed closely to the logic onlines 44, 46, respectively. In practice, network interface cards orgateways 50, 52 control this logic to within 10 μs and preferably within1-5 μs. A low accuracy network controls the individual power suppliesfor data from central control 18 through lines 42 m, 42 s, illustratedas provided by the gateways or interface cards. These lines contain datafrom remote areas (such as central control 18) which are not timesensitive and do not use the accuracy characteristics of the gateways.The highly accurate data for timing the switch reversal usesinterconnecting logic signals through network interface cards 50, 52.The system in FIG. 1 is a single cell for a single AC arc; however, theinvention is not limited to tandem electrodes wherein two or more ACarcs are created to fill the large gap found in pipe welding. However,the background system is shown for this application. Thus, the masterpower supply 30 for the first electrode receives a synchronizationsignal which determines the timing or phase operation of the system Sfor a first electrode, i.e. ARC 1. System S is used with other identicalsystems to generate ARCs 2, 3, and 4 timed by synchronizing outputs 84,86 and 88. This concept is schematically illustrated in FIG. 5. Thesynchronizing or phase setting signals 82-88 are shown in FIG. 1 withonly one of the tandem electrodes. An information network N comprising acentral control computer and/or web server 60 provides digitalinformation or data relating to specific power supplies in severalsystems or cells controlling different electrodes in a tandem operation.Internet information is directed to a local area network in the form ofan ethernet network 70 having local interconnecting lines 70 a, 70 b, 70c. Similar interconnecting lines are directed to each power supply usedin the four cells creating ARCs 1, 2, 3 and 4 of a tandem weldingoperation. The description of system or cell S applies to each of thearcs at the other electrodes. If AC current is employed, a master powersupply is used. In some instances, merely a master power supply is usedwith a cell specific synchronizing signal. If higher currents arerequired, the systems or cells include a master and slave power supplycombination as described with respect to system S of FIG. 1. In someinstances, a DC arc is used with two or more AC arcs synchronized bygenerator 80. Often the DC arc is the leading electrode in a tandemelectrode welding operation, followed by two or more synchronized ACarcs. A DC power supply need not be synchronized, nor is there a needfor accurate interconnection of the polarity logic and switching pointsor commands. Some DC powered electrodes maybe switched between positiveand negative, but not at the frequency of an AC driven electrode.Irrespective of the make-up of the arcs, ethernet or local area network70 includes the parameter information identified in a coded fashiondesignated for specific power supplies of the various systems used inthe tandem welding operation. This network also employs synchronizingsignals for the several cells or systems whereby the systems can beoffset in a time relationship. These synchronizing signals are decodedand received by a master power supply as indicated by line 40 in FIG. 1.In this manner, the AC arcs are offset on a time basis. Thesesynchronizing signals are not required to be as accurate as theswitching points through network interface cards or gateways 50, 52.Synchronizing signals on the data network are received by a networkinterface in the form of a variable pulse generator 80. The generatorcreates offset synchronizing signals in lines 84, 86 and 88. Thesesynchronizing signals dictate the phase of the individual alternatingcurrent cells for separate electrodes in the tandem operation.Synchronizing signals can be generated by interface 80 or actuallyreceived by the generator through the network 70. Network 70 merelyactivates generator 80 to create the delay pattern for the manysynchronizing signals. Also, generator 80 can vary the frequency of theindividual cells by frequency of the synchronizing pulses if thatfeature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe system as described in FIG. 1; however, preferred implementation ofthe system is set forth in FIG. 2 wherein power supply PSA is combinedwith controller and power supply 30 and power supply PSB is combinedwith controller and power supply 32. These two units are essentially thesame in structure and are labeled with the same numbers whenappropriate. Description of power supply PSA applies equally to powersupply PSB. Inverter 100 has an input rectifier 102 for receiving threephase line current L1, L2, and L3. Output transformer 110 is connectedthrough an output rectifier 112 to tapped inductor 120 for drivingopposite polarity switches Q1, Q2. Controller 140 a of power supply PSAand controller 140 b of PSB are essentially the same, except controller140 a outputs timing information to controller 140 b. Switching pointsor lines 142, 144 control the conductive condition of polarity switchesQ1, Q2 for reversing polarity at the time indicated by the logic onlines 142, 144, as explained in more detail in Stava U.S. Pat. No.6,111,216 incorporated by reference herein. The control is digital witha logic processor; thus, A/D converter 150 converts the currentinformation on feedback line 16 or line 26 to controlling digital valuesfor the level of output from error amplifier 152 which is illustrated asan analog error amplifier. In practice, this is a digital system andthere is no further analog signal in the control architecture. Asillustrated, however, amplifier has a first input 152 a from converter150 and a second input 152 b from controller 140 a or 140 b. The currentcommand signal on line 152 b includes the wave shape or waveformrequired for the AC current across the arc at weld station WS. This isstandard practice as taught by several patents of Lincoln Electric, suchas Blankenship U.S. Pat. No. 5,278,390, incorporated by reference. Seealso Stava U.S. Pat. No. 6,207,929, incorporated by reference. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. The shape of the waveform at the arcs is the voltage ordigital number at lines 152 b. The frequency of oscillator 164 isgreater than 18 kHz. The total architecture of this system is digitizedin the preferred embodiment of the present invention and does notinclude reconversion back into analog signal. This representation isschematic for illustrative purposes and is not intended to be limitingof the type of power supply used in practicing the present invention.Other power supplies could be employed.

A background system utilizing the concepts of FIGS. 1 and 2 areillustrated in FIGS. 3 and 4. Workpiece 200 is a seam in a pipe which iswelded together by tandem electrodes 202, 204 and 206 powered byindividual power supplies PS1, PS2, PS3, respectively. The powersupplies can include more than one power source coordinated inaccordance with the technology in Houston U.S. Pat. No. 6,472,634. Theillustrated embodiment involves a DC arc for lead electrode 202 and anAC arc for each of the tandem electrodes 204, 206. The created waveformsof the tandem electrodes are AC currents and include shapes created by awave shaper or wave generator in accordance with the previouslydescribed waveform technology. As electrodes 202, 204 and 206 are movedalong weld path WP a molten metal puddle P is deposited in pipe seam 200with an open root portion 210 followed by deposits 212, 214 and 216 fromelectrodes 202, 204 and 206, respectively. As previously described morethan two AC driven electrodes as will be described and illustrated bythe waveforms of FIG. 15, can be operated by the invention relating toAC currents of adjacent electrodes. The power supplies, as shown in FIG.4, each include an inverter 220 receiving a DC link from rectifier 222.In accordance with Lincoln waveform technology, a chip or internalprogrammed pulse width modulator stage 224 is driven by an oscillator226 at a frequency greater than 18 kHz and preferably greater than 20kHz. As oscillator 226 drives pulse width modulator 224, the outputcurrent has a shape dictated by the wave shape outputted from waveshaper 240 as a voltage or digital numbers at line 242. The shape inreal time is compared with the actual arc current in line 232 by a stageillustrated as comparator 230 so that the outputs on line 234 controlsthe shape of the AC waveforms. The digital number or voltage on line 234determines the output signal on line 224 a to control inverter 220 sothat the waveform of the current at the arc follows the selected profileoutputted from wave shaper 240. This is standard Lincoln waveformtechnology, as previously discussed. Power supply PS1 creates a DC arcat lead electrode 202; therefore, the output from wave shaper 240 ofthis power supply is a steady state indicating the magnitude of the DCcurrent. The present invention does not relate to the formation of a DCarc. To the contrary, the present invention is the control of thecurrent at two adjacent AC arcs for tandem electrodes, such aselectrodes 204, 206. In accordance with the invention, wave shaper 240involves an input 250 employed to select the desired shape or profile ofthe AC waveform. This shape can be shifted in real time by an internalprogramming schematically represented as shift program 252. Wave shaper240 has an output which is a priority signal on line 254. In practice,the priority signal is a bit of logic, as shown in FIG. 7. Logic 1indicates a negative polarity for the waveform generated by wave shaper240 and logic 0 indicates a positive polarity. This logic signal or bitcontroller 220 directed to the power supply is read in accordance withthe technology discussed in FIG. 16. The inverter switches from apositive polarity to a negative polarity, or the reverse, at a specific“READY” time initiated by a change of the logic bit on line 254. Inpractice, this bit is received from variable pulse generator 80 shown inFIG. 1 and in FIG. 5. The background welding system shown in FIGS. 3 and4 uses the shapes of AC arc currents at electrodes 204 and 206 to obtaina beneficial result, i.e. a generally quiescent molten metal puddle Pand/or synthesized sinusoidal waveforms compatible with transformerwaveforms used in arc welding. The electric arc welding system shown inFIGS. 3 and 4 have a program to select the waveform at “SELECT” program250 for wave shaper 240. The unique waveforms are used by the tandemelectrodes. One of the power supplies to create an AC arc isschematically illustrated in FIG. 5. The power supply or source iscontrolled by variable pulse generator 80, shown in FIG. 1. Signal 260from the generator controls the power supply for the first arc. Thissignal includes the synchronization of the waveform together with thepolarity bit outputted by the wave shaper 240 on line 254. Lines 260a-260 n control the desired subsequent tandem AC arcs operated by thewelding system of the present invention. The timing of these signalsshifts the start of the other waveforms. FIG. 5 merely shows therelationship of variable pulse generator 80 to control the successivearcs as explained in connection with FIG. 4.

In the welding system of Houston U.S. Pat. No. 6,472,634, the ACwaveforms are created as shown in FIG. 6 wherein the wave shaper for arcAC1 at electrode 204 creates a signal 270 having positive portions 272and negative portions 274. The second arc AC2 at electrode 206 iscontrolled by signal 280 from the wave shaper having positive portions282 and negative portions 284. These two signals are the same, but areshifted by the signal from generator 80 a distance x, as shown in FIG.6. The waveform technology created current pulses or waveforms at one ofthe arcs are waveforms having positive portions 290 and negativeportions 292 shown at the bottom portion of FIG. 6. A logic bit from thewave shaper determines when the waveform is switched from the positivepolarity to the negative polarity and the reverse. In accordance withthe disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated byreference herein) pulse width modulator 224 is generally shifted to alower level at point 291 a and 291 b. Then the current reduces untilreaching a fixed level, such as 100 amps. Consequently, the switcheschange polarity at points 294 a and 294 b. This produces a vertical lineor shape 296 a, 296 b when current transitioning between positiveportion 290 and negative portion 292. This is the system disclosed inthe Houston patent where the like waveforms are shifted to avoidmagnetic interference. The waveform portions 290, 292 are the same atarc AC1 and at arc AC2. This is different from the present inventionwhich relates to customizing the waveforms at arc AC1 and arc AC2 forpurposes of controlling the molten metal puddle and/or synthesizing asinusoidal wave shape in a manner not heretofore employed. Thedisclosure of FIG. 6 is set forth to show the concept of shifting thewaveforms. The same switching procedure to create a vertical transitionbetween polarities is used in the preferred embodiment of the presentinvention. Converting from the welding system shown in FIG. 6 to animbalance waveformis generally shown in FIG. 7. The logic on line 254 isillustrated as being a logic 1 in portions 300 and a logic 0 in portions302. The change of the logic or bit numbers signals the time when thesystem illustrated in FIG. 16 shifts polarity. This is schematicallyillustrated in the lower graph of FIG. 6 at points 294 a, 294 b. Waveshaper 240 for each of the adjacent AC arcs has a first wave shape 310for one of the polarities and a second wave shape 312 for the otherpolarity. Each of the waveforms 310, 312 are created by the logic online 234 taken together with the logic on line 254. Thus, pulses 310,312 as shown in FIG. 7, are different pulses for the positive andnegative polarity portions. Each of the pulses 310, 312 are created byseparate and distinct current pulses 310 a, 312 a as shown. Switchingbetween polarities is accomplished as illustrated in FIG. 6 where thewaveforms generated by the wave shaper are shown as having the generalshape of waveforms 310, 312. Positive polarity controls penetration andnegative polarity controls deposition. The positive and negative pulsesof a waveform are different and the switching points are controlled sothat the AC waveform at one arc is controlled both in the negativepolarity and the positive polarity to have a specific shape created bythe output of wave shaper 240. The waveforms for the arc adjacent to thearc having the current shown in FIG. 7 is controlled differently toobtain the advantages illustrated best in FIG. 8. The waveform at arc AC1 is in the top part of FIG. 8. It has positive portions 320 shown bycurrent pulses 320 a and negative portions 322 formed by pulses 322 a.Positive portion 320 has a maximum magnitude a and width or time periodb. Negative portion 322 has a maximum magnitude d and a time or periodc. These four parameters are adjusted by wave shaper 240. In theillustrated embodiment, arc AC2 has the waveform shown at the bottom ofFIG. 8 where positive portion 330 is formed by current pulses 330 a andhas a height or magnitude a′ and a time length or period b′. Negativeportion 332 is formed by pulses 332 a and has a maximum amplitude b′ anda time length c′. These parameters are adjusted by wave shaper 240. Inaccordance with the invention, the waveform from the wave shaper on arcAC1 is out of phase with the wave shape for arc AC2. The two waveformshave parameters or dimensions which are adjusted so that (a) penetrationand deposition is controlled and (b) there is no long time during whichthe puddle P is subjected to a specific polarity relationship, be it alike polarity or opposite polarity. This concept in formulating the waveshapes prevents long term polarity relationships as explained by theshowings in FIGS. 9 and 10. In FIG. 9 electrodes 204, 206 have likepolarity, determined by the waveforms of the adjacent currents at anygiven time. At that instance, magnetic flux 350 of electrode 204 andmagnetic flux 352 of electrode 206 are in the same direction and canceleach other at center area 354 between the electrodes. This causes themolten metal portions 360, 362 from electrodes 204, 206 in the moltenpuddle P to move together, as represented by arrows c. This inwardmovement together or collapse of the molten metal in puddle P betweenelectrodes 204 will ultimately cause an upward gushing action, if notterminated in a very short time, i.e. less than about 20 ms. As shown inFIG. 10, the opposite movement of the puddle occurs when the electrodes204, 206 have opposite polarities. Then, magnetic flux 370 and magneticflux 372 are accumulated and increased in center portion 374 between theelectrodes. High forces between the electrodes causes the molten metalportions 364, 366 of puddle P to retract or be forced away from eachother. This is indicated by arrows r. Such outward forcing of the moltenmetal in puddle P causes disruption of the weld bead if it continues fora substantial time which is generally less than 10 ms. As can be seenfrom FIGS. 9 and 10, it is desirable to limit the time during which thepolarity of the waveform at adjacent electrodes is either the samepolarity or opposite polarity. The waveform, such as shown in FIG. 6,accomplishes the objective of preventing long term concurrence ofspecific polarity relationships, be it like polarities or oppositepolarities. As shown in FIG. 8, like polarity and opposite polarity isretained for a very short time less than the cycle length of thewaveforms at arc AC1 and arc AC2. This positive development ofpreventing long term occurrence of polarity relationships together withthe novel concept of pulses having different shapes and differentproportions in the positive and negative areas combine to control thepuddle, control penetration and control deposition in a manner notheretofore obtainable in welding with a normal transformer powersupplies or normal use of Lincoln waveform technology.

In FIG. 11 the positive and negative portions of the AC waveform fromthe wave shaper 240 are synthesized sinusoidal shapes with a differentenergy in the positive portion as compared to the negative portion ofthe waveforms. The synthesized sine wave or sinusoidal portions of thewaveforms allows the waveforms to be compatible with transformer weldingcircuits and compatible with evaluation of sine wave welding. In FIG.11, waveform 370 is at arc AC1 and waveform 372 is at arc AC2. Thesetandem arcs utilize the AC welding current shown in FIG. 11 wherein asmall positive sinusoidal portion 370 a controls penetration at arc AC1while the larger negative portion 370 b controls the deposition of metalat arc AC1. There is a switching between the polarities with a change inthe logic bit, as discussed in FIG. 7. Sinusoidal waveform 370 plungesvertically from approximately 100 amperes through zero current as shownin by vertical line 370 c. Transition between the negative portion 370 band positive portion 370 a also starts a vertical transition at theswitching point causing a vertical transition 370 d. In a like manner,phase shifted waveform 372 of arc AC2 has a small penetration portion372 a and a large negative deposition portion 372 b. Transition betweenpolarities is indicated by vertical lines 372 c and 372 d. Waveform 372is shifted with respect to waveform 370 so that the dynamics of thepuddle are controlled without excessive collapsing or repulsion of themolten metal in the puddle caused by polarities of adjacent arcs AC1,AC2. In FIG. 11, the sine wave shapes are the same and the frequenciesare the same. They are merely shifted to prevent a long term occurrenceof a specific polarity relationship.

In FIG. 12 waveform 380 is used for arc AC1 and waveform 372 is used forarc AC2. Portions 380 a, 380 b, 382 a, and 382 b are sinusoidalsynthesized and are illustrated as being of the same general magnitude.By shifting these two waveforms 90°, areas of concurrent polarity areidentified as areas 390, 392, 394 and 396. By using the shiftedwaveforms with sinusoidal profiles, like polarities or oppositepolarities do not remain for any length of time. Thus, the molten metalpuddle is not agitated and remains quiescent. This advantage is obtainedby using the present invention which also combines the concept of adifference in energy between the positive and negative polarity portionsof a given waveform. FIG. 12 is illustrative in nature to show thedefinition of concurrent polarity relationships and the fact that theyshould remain for only a short period of time. To accomplish thisobjective, another embodiment of the present invention is illustrated inFIG. 13 wherein previously defined waveform 380 is combined withwaveform 400, shown as the sawtooth waveform of arc AC2(a) or thepulsating waveform 402 shown as the waveform for arc AC2(b). Combiningwaveform 380 with the different waveform 400 of a different waveform 402produces very small areas or times of concurrent polarity relationships410, 412, 414, etc. In FIG. 14 the AC waveform generated at one arc isdrastically different than the AC waveform generated at the other arc.This same concept of drastically different waveforms for use in thepresent invention is illustrated in FIG. 14 wherein waveform 420 is anAC pulse profile waveform and waveform 430 is a sinusoidal profilewaveform having about one-half the period of waveform 420. Waveform 420includes a small penetration positive portion 420 a and a largedeposition portion 420 b with straight line polarity transitions 420 c.Waveform 430 includes positive portion 430 a and negative portion 430 bwith vertical polarity transitions 430 c. By having these two differentwaveforms, both the synthesized sinusoidal concept is employed for oneelectrode and there is no long term concurrent polarity relationship.Thus, the molten metal in puddle P remains somewhat quiescent during thewelding operation by both arcs AC1, AC2.

In FIG. 15 waveforms 450, 452, 454 and 456 are generated by the waveshaper 240 of the power supply for each of four tandem arcs, arc AC1,arc AC2, arc AC3 and arc AC4. The adjacent arcs are aligned as indicatedby synchronization signal 460 defining when the waveforms correspond andtransition from the negative portion to the positive portion. Thissynchronization signal is created by generator 80 shown in FIG. 1,except the start pulses are aligned. In this embodiment of the inventionfirst waveform 450 has a positive portion 450 a, which is synchronizedwith both the positive and negative portion of the adjacent waveform452, 454 and 456. For instance, positive portion 450 a is synchronizedwith and correlated to positive portion 452 a and negative portion 452 bof waveform 452. In a like manner, the positive portion 452 a ofwaveform 452 is synchronized with and correlated to positive portion 454a and negative portion 454 b of waveform 454. The same relationshipexist between positive portion 454 a and the portions 456 a, 456 b ofwaveform 456. The negative portion 450 b is synchronized with andcorrelated to the two opposite polarity portions of aligned waveform452. The same timing relationship exist between negative portion 452 band waveform 454. In other words, in each adjacent arc one polarityportion of the waveform is correlated to a total waveform of theadjacent arc. In this manner, the collapse and repelling forces ofpuddle P, as discussed in connection with FIGS. 9 and 10, aredynametically controlled. One or more of the positive or negativeportions can be synthesized sinusoidal waves as discussed in connectionwith the waveforms disclosed in FIGS. 11 and 12.

As indicated in FIGS. 1 and 2, when the master controller of switches isto switch, a switch command is issued to master controller 140 a ofpower supply 30. This causes a “kill” signal to be received by themaster so a kill signal and polarity logic is rapidly transmitted to thecontroller of one or more slave power supplies connected in parallelwith a single electrode. If standard AC power supplies are used withlarge snubbers in parallel with the polarity switches, the slavecontroller or controllers are immediately switched within 1-10 μs afterthe master power supply receives the switch command. This is theadvantage of the high accuracy interface cards or gateways. In practice,the actual switching for current reversal of the paralleled powersupplies is not to occur until the output current is below a givenvalue, i.e. about 100 amperes. This allows use of smaller switches.

The implementation of the switching for all power supplies for a singleAC arc uses the delayed switching technique where actual switching canoccur only after all power supplies are below the given low currentlevel. The delay process is accomplished in the software of the digitalprocessor and is illustrated by the schematic layout of FIG. 16. Whenthe controller of master power supply 500 receives a command signal asrepresented by line 502, the power supply starts the switching sequence.The master outputs a logic on line 504 to provide the desired polarityfor switching of the slaves to correspond with polarity switching of themaster. In the commanded switch sequence, the inverter of master powersupply 500 is turned off or down so current to electrode E is decreasedas read by hall effect transducer 510. The switch command in line 502causes an immediate “kill” signal as represented by line 512 to thecontrollers of paralleled slave power supplies 520, 522 providingcurrent to junction 530 as measured by hall effect transducers 532, 534.All power supplies are in the switch sequence with inverters turned offor down. Software comparator circuits 550, 552, 554 compare thedecreased current to a given low current referenced by the voltage online 556. As each power supply decreases below the given value, a signalappears in lines 560, 562, and 564 to the input of a sample and holdcircuits 570, 572, and 574, respectively. The circuits are outputted bya strobe signal in line 580 from each of the power supplies. When a setlogic is stored in a circuit 570, 572, and 574, a YES logic appears onlines READY¹, READY², and READY³ at the time of the strobe signal. Thissignal is generated in the power supplies and has a period of 25 μs;however, other high speed strobes could be used. The signals aredirected to controller C of the master power supply, shown in dashedlines in FIG. 8. A software ANDing function represented by AND gate 580has a YES logic output on line 582 when all power supplies are ready toswitch polarity. This output condition is directed to clock enableterminal ECLK of software flip flop 600 having its D terminal providedwith the desired logic of the polarity to be switched as appearing online 504. An oscillator or timer operated at about 1 MHz clocks flipflop by a signal on line 602 to terminal CK. This transfers the polaritycommand logic on line 504 to a Q terminal 604 to provide this logic inline 610 to switch slaves 520, 522 at the same time the identical logicon line 612 switches master power supply 500. After switching, thepolarity logic on line 504 shifts to the opposite polarity while masterpower supply awaits the next switch command based upon the switchingfrequency. Other circuits can be used to effect the delay in theswitching sequence; however, the illustration in FIG. 16 is the presentscheme.

As so far described in FIGS. 1-16, the welder, and control system forthe welder to accomplish other advantageous features is submitted asbackground information. This description explains the background, notprior art, to the present invention. This background technology has beendeveloped by The Lincoln Electric Company, assignee of the presentapplication. This background description is not necessarily prior art,but is submitted for explanation of the specific improvement in suchwaveform technology welders, as accomplished by the present inventionshown in FIGS. 17 AND 18.

The welder and/or welding system as shown in FIGS. 4 and 5, is operatedby control program 700 constructed in accordance with the presentinvention. Program 700 is illustrated in FIG. 17, where welder W has awave shaper 240 set to a general type of weld waveformby a selectnetwork 250. The selected waveform is the desired AC waveform toperform, by a succession of waveforms, a given welding process. Inaccordance with the invention, waveform control program 700 has aprofile control network 710 to set the desired general profile of thewaveform and a magnitude control circuit 712 to adjust the energy orpower of the waveform without substantially changing the set profile.

In accordance with the invention, the program or control network 700 isconnected to the wave shaper 240 to control the exact general profile ofeach individual waveform in the succession of waveforms constituting anAC welding process. To accomplish this objective of accurate and precisesynergistic setting of the waveform general profile, four separateprofile parameters are adjusted individually. The first parameter isfrequency set into the waveform profile by circuit 720 manually orautomatically adjusted by interface network 722 to produce a set valueon an output represented as line 724. This value controls the setfrequency of the waveform profile. Of course, this is actually theperiod of the waveform. In a like manner, the duty cycle of the waveformis controlled by circuit 730 having an adjustable interface network 732and an output line 734 for developing a value to control therelationship between the positive half cycle and the negative halfcycle. This profile parameter is set by the logic or data on line 754from circuit 730. By the signal or data on line 724 and the data on line734, the AC profile of the waveform is set. This does not relate to theenergy level of the individual portions of the waveform, but merely thegeneral fixed profile of the waveform. To control the up ramp rate ofthe waveform there is provided a circuit 742 having a manual orautomatic adjusting network 742 and an output signal on line 744 forsetting the rate at which the set profile of the waveform changes fromnegative to a positive polarity. In a like manner, a down ramp circuit750 is provided with an adjusting interface 752 and an output line 754.The magnitudes of the values on lines 724, 734, 744 and 754 set thegeneral profile of the individual waveform. In accordance with theinvention, at least two of these parameter profiles are set together;however, preferably all of the profile parameters are set to define ageneral waveform profile.

To control the general profile of the waveform for the purposes of theenergy or power transmitted by each individual waveform in the weldingprocess, the present invention includes magnitude circuit or network 712divided into two individual sections 760, 762. These sections of themagnitude circuit control the energy or other power related level of thewaveform during each of the polarities without substantially affectingthe general profile set by profile control network 710. In accordancewith the illustrated embodiment of the invention, section 760 includes alevel control circuit 770 which is manually adjusted by an interfacenetwork 772 to control the relationship between an input value on line774 and an output value on line 776. Level control circuit 770 isessentially a digital error amplifier circuit for controlling thecurrent, voltage and/or power during the positive portion of thegenerated set waveform profile. Selector 250 a shifts circuit 770 intoeither the current, voltage or power mode. Section 760 controls theenergy, or power or other heat level during the positive portion of thewaveform with changing the general profile set by network 710. In a likemanner, second section 762 has a digital error amplifier circuit 760that is set or adjusted by network 782 so that the value on input line784 controls the level or signal on output line 786. Consequently, thedigital level data on lines 776 and 786 controls the current, voltageand/or power during each of the half cycles set by profile controlnetwork 710.

In accordance with another aspect of the invention, wave shaper 240 iscontrolled by only magnitude control circuit 712 and the profile is setby network or program 250 used in the background system shown in FIGS. 4and 5. Network 250 does not set the general profile, but selects knowntypes of waveforms. The enhanced advantage of the present invention isrealized by setting all profile parameters using circuits 720, 730, 740and 750 together with the magnitude circuits 770, 780. Of course, awaveform controlled by any one of these circuits is an improvement overthe background technology. The invention is a synergistic control of allof the profile parameters and magnitude values during each polarity ofthe AC waveform.

To explain the operation of the invention two waveforms areschematically illustrated in FIG. 18. Waveform 800 has a positiveportion 802 and a negative portion 804, both produced by a series ofrapidly created current pulses 800 a. Waveform 800 is illustrated asmerely a square wave to illustrate control of the frequency or period ofthe waveform and the ratio of the positive portion 802 to the negativeportion 804. These parameters are accurately set by using the inventionto modify the type of waveform heretofore merely selected by network450. In this schematic representation of the waveform, the up ramp rateand the down ramp rate are essentially zero. Of course, the switchingconcept taught in Stava U.S. Pat. No. 6,111,216 would be employed forshifting between positive and negative waveform portions to obtain theadvantages described in the Stava patent. Second illustrated waveform810 has a frequency f, a positive portion 812 and a negative portion814. In this illustration, the up ramp rate 816 is controlledindependently of the down ramp rate 818. These ramp rates areillustrated as arrows to indicate they exist at the leading and trailingedges of the waveform during shifts between polarities. The presentinvention relates to setting the exact profile of the individualwaveforms by circuits 720, 730, 740 and 750. The invention involvessetting several parameters to essentially “paint” the waveform into adesired general profile. A very precise welding process using a setgeneral profile for the AC waveform is performed by a waveformtechnology controlled welder using the present invention.

1. An electric arc welder for creating a succession of AC waveformsbetween an electrode and workpiece by a power source comprising an highfrequency switching device for creating individual waveforms in saidsuccession of waveforms, each of said individual waveforms having aprofile determined by the magnitude of each of a large number of shortcurrent pulses generated at a frequency of at least 18 kHz by a pulsewidth modulator with the magnitude of said current pulses controlled bya wave shaper and the polarity of any portion of said individualwaveforms determined by the data of a polarity signal, a profile controlnetwork for establishing the general profile of an individual waveformby setting more than one profile parameter of an individual waveform,said parameters selected from the class consisting of frequency, dutycycle, up ramp rate and down ramp rate and a magnitude circuit foradjusting the individual waveform to set total current, voltage and/orpower without substantially affecting the general fixed profile.
 2. Anelectric arc welder as defined in claim 1 wherein said magnitude circuithas a first section for adjusting said individual waveform during thepositive polarity of said one waveform and a second section foradjusting said individual waveform during the negative polarity of saidAC waveform.
 3. An electric arc welder as defined in claim 2 including adevice for selecting current, voltage or power in said first section ofsaid magnitude circuit.
 4. An electric arc welder as defined in claim 3including a device for selecting current, voltage or power in saidsecond section of said magnitude circuit.
 5. An electric arc welder asdefined in claim 2 including a device for selecting current, voltage orpower in said second section of said magnitude circuit.
 6. An electricarc welder as defined in claim 5 wherein said profile control networksets at least three of said profile parameters.
 7. An electric arcwelder as defined in claim 4 wherein said profile control network setsat least three of said profile parameters.
 8. An electric arc welder asdefined in claim 3 wherein said profile control network sets at leastthree of said profile parameters.
 9. An electric arc welder as definedin claim 2 wherein said profile control network sets at least three ofsaid profile parameters.
 10. An electric arc welder as defined in claim1 wherein said profile control network sets at least three of saidprofile parameters.
 11. An electric arc welder as defined in claim 5wherein said profile control network set all four of said named profileparameters.
 12. An electric arc welder as defined in claim 4 whereinsaid profile control network set all four of said named profileparameters.
 13. An electric arc welder as defined in claim 3 whereinsaid profile control network set all four of said named profileparameters.
 14. An electric arc welder as defined in claim 2 whereinsaid profile control network set all four of said named profileparameters.
 15. An electric arc welder as defined in claim 1 whereinsaid profile control network set all four of said named profileparameters.
 16. A method of electric arc welding by creating asuccession of AC waveforms between an electrode and workpiece by a powersource comprising an high frequency switching device for creatingindividual waveforms in said succession of waveforms, each of saidindividual waveforms having a profile determined by the magnitude ofeach of a large number of short current pulses generated at a frequencyof at least 18 kHz by a pulse width modulator with the magnitude of saidcurrent pulses controlled by a wave shaper, said method comprising: (a)determining the polarity of any portion of said individual waveforms bythe data of a polarity signal; (b) establishing the general profile ofan individual waveform by setting more than one profile parameter of anindividual waveform, said parameters selected from the class consistingof frequency, duty cycle, up ramp rate and down ramp rate; and, (c)adjusting the waveform profile to set total magnitude of current,voltage and/or power without substantially changing the general profile.17. A method as defined in claim 16 including the acts of: (d) adjustingthe magnitude of said individual waveform during the positive polarityof said AC waveform; and, (e) adjusting the magnitude of said individualwaveform during the negative polarity of said AC waveform.
 18. A methodas defined in claim 17 including the act of: (f) selecting current,voltage or power for magnitude control during said positive polarity.19. A method as defined in claim 17 including the act of: (g) selectingcurrent, voltage or power for magnitude control during said negativepolarity.
 20. A method as defined in claim 16 including the act of: (d)adjusting the magnitude of said individual waveform during the positivepolarity of said AC waveform.
 21. A method as defined in claim 16including the act of: (d) adjusting the magnitude of said individualwaveform during the negative polarity of said AC waveform.
 22. Anelectric arc welder for creating a succession of AC waveforms between anelectrode and a workpiece by a power source comprising an high frequencyswitching device for creating individual waveforms in said succession ofwaveforms, each of said individual waveforms having a profile determinedby the magnitude of each of a large number of short current pulsesgenerated at a frequency of at least 18 kHz by a pulse width modulatorwith the magnitude of said current pulses controlled by a wave shaperand the polarity of any portion of said individual waveform determinedby the data of a polarity signal, and a magnitude circuit for adjustingthe individual waveform to a set condition of current, voltage or power.23. An electric arc welder as defined in claim 22 wherein said magnitudecircuit includes an input selector to set said magnitude circuit to adesired polarity.
 24. An electric arc welder as defined in claim 23including a profile control network to control the general profile ofsaid individual waveform.
 25. An electric arc welder as defined in claim24 wherein said profile control network controls more than one profileparameter of an individual waveform profile, said parameters selectedfrom the class consisting of frequency, duty cycle up ramp rate and downramp rate.
 26. An electric arc welder as defined in claim 22 including aprofile control network to control the general profile of saidindividual waveform.
 27. An electric arc welder as defined in claim 26wherein said profile control network controls more than one profileparameter of an individual waveform profile, said parameters selectedfrom the class consisting of frequency, duty cycle up ramp rate and downramp rate.
 28. An electric arc welder for creating a succession of ACwaveforms between an electrode and a workpiece by a power sourcecomprising an high frequency switching device for creating individualwaveforms in said succession of waveforms, each of said individualwaveforms having a profile determined by the magnitude of each of alarge number of short current pulses generated at a frequency of atleast 18 kHz by a pulse width modulator with the magnitude of saidcurrent pulses controlled by a wave shaper and the polarity of anyportion of said individual waveform determined by the data of a polaritysignal, and a profile control network to control the general profile ofsaid individual waveform.